The present invention is related to an image forming machine such as a copying machine, printer, facsimile machine, and combined machine of them using an electrophotographic process, specifically to an image forming machine composed such that a unit integrating at least an electric charging device and an image carrier device is detachably mounted or only an image carrier device is detachably mounted and a mechanism is provided for removing the electric charge accumulated in the process of detaching or attaching the unit from or to the image forming machine.
In the field of image forming machines such as copying machines, printers, facsimile machines, and combined machines aimed for personal use, a unit integrating at least an electric charging device and an image carrier device and mounted detachably to a body of the image forming machine is used to ease the handling of the machine by making it possible for users to perform the maintenance of the machine.
However, in the image forming machine in which the unit like this or only the image carrier device (photoreceptor) is detachable, when a sheet is jammed during image formation in the state the sheet is nipped between a photoreceptor drum and transfer roller due to the occurrence of malfunction in a clutch, inadequate feeding of a copy sheet due to the skew of the sheet, slipping of the sheet, etc., can occur while the image carrier device is still charged as the charging device for charging the image carrier device had been working until just before the jam. If the user detaches the unit or image carrier device from the image forming machine body to remove the jammed paper sheet and again sets the unit or image carrier device to the machine body after the jammed sheet is removed, spark discharge occurs and noise is produced when an electrically conductive shaft of the image carrier device contacts with a grounding member provided to the image forming machine body. Actually a phenomenon occurs in which the machine's initialization program falls into an endless loop and printing becomes impossible when electrical discharging occurs while the initialization program for initializing the image forming machine was working.
A similar phenomenon will happen in an image forming machine, in which a casing of the machine is configured such that an outer part thereof is capable of opening and closing, when a safety measure function works by intentionally opening an outer part of the casing, and electric power supply to apply high d.c. voltage to a motor, clutch, charger of the drum, etc., is shut down. That is, if electrical discharging like this occurs, a noise signal induced by the discharging directly enters a lead wire strung around the inside of the image forming machine or a circuit of a main board and interferes with the execution of an initialization program in a CPU, and a ready signal which is to be sent forth when the initialization program works normally is not sent out. Such a phenomenon tends to occur in the case resin material is used in many of the component parts and electrostatic guard is not sufficient.
As to a method for eliminating electric charge on the unit or image carrier device, an image forming machine is disclosed for example in Japanese Laid-Open Patent Application No. 9-90690 (hereafter referred to patent literature 1) which is composed such that, before a process cartridge reaches the required position, a photoreceptor drum or developing sleeve of a developing device is allowed to contact an electrode provided in the image forming machine to let a static charge go off to a machine body or the photoreceptor drum and developing sleeve are together grounded in order to equalize an electric potential of them with that of the machine body. By composition, a charged memory, which is induced due to the phenomenon that the photoreceptor drum or developing sleeve becomes charged by a static charge caused by any reason and electric discharging occurs between the photoreceptor drum and an electrically conductive member located adjacent to the photoreceptor drum when replacing the photoreceptor drum unit or other unit, is prevented from being produced in the photoreceptor drum.
However, the image forming machine disclosed in patent literature 1 is of the composition for preventing a charged memory, which is induced due to the phenomenon that the photoreceptor drum or developing sleeve becomes charged by the static charge caused by any reason and electric discharging occurs between the photoreceptor drum and the electrical conductive member located adjacent to the photoreceptor drum, from being produced in the photoreceptor drum, and therefore, although the buildup of the charged memory can be prevented, the noise accompanying the discharging is not taken into consideration. Therefore, the phenomenon that the initialization program falls into an endless loop cannot be prevented.
Accordingly, the object of the present invention is to provide an image forming machine composed such that the unit or image carrier device (photoreceptor) is detachably mounted to the machine, wherein even when the unit or image carrier device (photoreceptor) is detached for removing a jammed copy sheet and again attached in the state the image carrier device (photoreceptor) is charged, the influence caused by the noise due to electrical discharging can be suppressed.